Very large burner assemblies are used in a variety of applications. Such applications include, but are not limited to, heating air for air heaters and dryers, heating water to generate steam in boilers, or as part of combined cycle systems. Combined cycle systems typically generate both electricity and steam. In such combined cycle systems, a gas turbine typically generates the electrical power by burning a gaseous hydrocarbon fuel with air.
The present disclosure relates to particular burners, namely Low NOX burners; and the general term, “NOX” (nitrogen oxides) is used to describe a group of molecules that contain varying amounts of nitrogen and oxygen at certain ratios. NOX generally forms at high temperatures during fossil fuel combustion of some sort. In the United States, the primary sources of NOx Emissions are motor vehicles, power plants, and other commercial, industrial, and residential sources that combust fossil fuels. Direct NOX emissions from these sources include several different forms, such as nitrogen dioxide (NO2), nitrous oxide (N2O), and nitric oxide (NO), however, NOX generated during combustion is primarily produced in the form of NO. NOX emissions react with other compounds, such as those compounds considered or classified as volatile organic compounds in the troposphere to form secondary products that include ozone (O3), nitric acid (HNO3), nitrate particles, and the like. NOX emissions are generally considered to be air pollutants by themselves, as well as precursors to the formation of ozone (i.e., smog) and acid rain.
To protect public health, concentrations of NOX and ozone in the ambient atmosphere are often subject to air quality standards established in the United States by the Environmental Protection Agency (EPA). Because of the potentially negative health and environmental impacts associated with NOX emissions and their role in generating tropospheric ozone, NOX emissions producers are often highly regulated by the EPA, as well as by state and local environmental authorities. Regulations by federal and state authorities have engendered the development of low NOX burners for industrial applications. One example of a low NOX burner is described in U.S. Pat. No. 5,460,512. One version of this burner, commercially referred to as a QLN™ burner, is available from John Zink Company, LLC (www.johnzink.com) and provides for reduced NOX emissions.
One way to reduce NOX emissions in known burner systems is by introducing inert gases (e.g. CO2, H2O) into a combustion reaction to reduce peak flame temperature. Most commonly, this type of reduction is accomplished by recirculating direct products of combustion, such as flue exhaust gases, back into a combustion process, and is commonly referred to as Flue Gas Recirculation (FGR). Alternatively, exhaust gases from gas turbines may be used for combustion.
As noted above, in combined cycle systems, gas turbines burn hydrocarbon gases to generate electricity. Due to certain design constraints and operating requirements of gas turbines, the combustion process usually only partially depletes the available oxygen in air. Consequently, the resulting Turbine Exhaust Gas (TEG) often contains an elevated concentration of oxygen compared to typical exhaust gas found in boilers. This relatively large quantity of oxygen in TEG can be used as an oxidizer source for subsequent downstream fuel combustion.
Such downstream fuel combustion typically involves placing burners across a cross-section of a TEG exhaust duct. These burners, commonly referred to as duct burners, further deplete the TEG oxygen and generate sensible heat or thermal energy, which elevates the exhaust gas temperature. A Heat Recovery Steam Generator (HRSG) recovers the residual heat (present when exiting the turbine) of the TEG and the sensible heat added by the duct burner and uses these sources of heat to produce steam. Alternatively, and less commonly, the TEG can be ducted to a standard burner and boiler.